This is a small trick and it is, conceptually not new. It is common practice to add version numbers to resource files of a website. These are image-, CSS- and Javascript files. The reason to do so is to make sure users do get new versions of the files when you change them instead of when their browser decides to flush its cache. And you certainly don't want to tell your visitors to do a shift-reload for each small update you do. So you could do something like
<script type="text/javascript" charset="utf-8" src="prototype1.50.js"></script>
and update the version number whenever you change things. This is a maintenance nightmare, though, because you'll have multiple versions of the same file lingering around next to each other and all the beauty of version control (You do use it, right?) is lost.
What you can do instead, is adding a GET-parameter to the filename, like this
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